The present invention relates generally to integrated circuit packages. More specifically, the present invention relates to packaging of die having staggered bond pads into grid array-type integrated circuit packages.
Current industry emphasis on decreased size and increased functionality of semiconductor dice has resulted in the continuing development of integrated circuit dice having a high density of active circuits. Conventionally, the logic circuitry of the die is formed on the interior portion of the die and a plurality of input/output (I/O) devices or cells are located around the periphery of the die. Each I/O cell, typically, is connected to at least one bond pad fabricated at the surface of the die that serves as the input/output (I/O) contact for that cell.
Placement of the bond pads along the edges of each side of the die allow for connection, for example, by bonding wires, of the bond pads to electrical contacts on another substrate, such as bonding rings or bond fingers on a package substrate. Bond pads are conventionally arranged in an in-line arrangement or in a staggered arrangement.
FIG. 1 is a diagrammatic illustration of a portion of a die having an in-line arrangement of bond pads. In an in-line arrangement, the bond pads 104 are located along the periphery of the die 102 in a single row. Spacing of the bond pads 104 may be described in terms of a pad pitch, or the center-to-center spacing of the pads. For example, pad pitch 106 of the bond pads 104, may be, for example, 75 microns.
In some other dice, especially high-density dice, the bond pads may be arranged in a staggered arrangement resulting in multiple rows of bond pads located at the edges of the die. Staggering the bond pads permits more bond pads to be located on the die over that of an in-line arrangement. The location of a bond pad interior to the die, e.g., an inner bond pad, relative to the bond pads nearest the edge of the die, e.g., outer bond pads, may be described as being xe2x80x9cperfectlyxe2x80x9d staggered or xe2x80x9cnon-perfectlyxe2x80x9d staggered.
FIG. 2 is a diagrammatic illustration of a portion of a die having staggered bond pads in a xe2x80x9cperfectxe2x80x9d staggered arrangement. As illustrated, the inner bond pads 204 are staggered relative to the outer bond pads 206 in that they are located interior to the die 202 from the outer bond pads 206 and are not xe2x80x9cin-linexe2x80x9d with the outer bond pads 206. In this example, the inner bond pads 204 are arranged in a xe2x80x9cperfectxe2x80x9d staggered arrangement relative to the outer bond pads 206 as they are located interior to and directly between the outer bond pads 206, i.e., in the spaces. Although the pad pitch 208 between the outer bond pads 206 may be the same as in the in-line arrangement earlier described with reference to FIG. 1, e.g., 75 microns, the stagger of the additional row of inner bond pads 204 may result in an smaller overall effective pad pitch, for example, 45 microns. Thus, a greater density of bond pads may be located on the same size die with a staggered arrangement of bond pads over that of a die having an in-line arrangement of bond pads.
FIG. 3 is a diagrammatic illustration of a portion of a die having staggered bond pads in a xe2x80x9cnon-perfectxe2x80x9d staggered arrangement. In this example, the inner bond pads 304 of the die 302 are not located directly between the outer bond pads 306, but are horizontally offset relative to the outer bond pads 306 so that, with increasing offset from the space between the outer bond pads 306, portions of the inner bond pads 304 become located behind the outer bond pads 306. The offset may be to such a large degree that an inner bond pad 304 is directly aligned behind an outer bond pad 306.
As a staggered bond pad arrangement on a die provides greater bond pad density over that of most similarly sized die having in-line die arrangements, high-density dice are increasingly being designed with staggered bond pad arrangements. A design consideration, however, with the staggered arrangement is the possibility of wire crossing and shorting between bonding wires exiting from the inner bond pads with those bonding wires exiting from the outer bond pads when the die is attached to another substrate, such as a package substrate.
One type of packaging that is widely used in packaging a high-density die is a grid array-type package. There are many designs of grid array-type packages, for example, pin grid array packages and ball grid array packages. Generally, some packages mount the die on the surface of the package substrate, for example, a plastic ball grid array package; while, some others, mount the die in a die cavity formed in the substrate, for example, an enhanced ball grid array package.
When packaging a die, connections of the die to the conductive layers of the substrate are typically made by wire bonding the bond pad of the die to an associated bonding site, such as bond fingers or bonding rings, on the package substrate. With a die having an in-line arrangement of bond pads, there is usually a low risk of short circuits due to the bonding wires contacting each other as the bond pads are horizontally separated by the spacing between the bond pads and there is no crossing over of bonding wires from inner bond pads.
With a die having a staggered arrangement of bond pads, wire contact between bonding wires from inner bond pads which cross over bonding wires from outer pads is a concern. In some packages, the height of the wire loop of the bonding wire exiting the inner bond pad can be increased over that of the height of the wire loop of the bonding wire exiting the outer bond pad to provide vertical separation. However, in some other packages, this height adjustment can be constrained to such a degree that the particular package design cannot be used in packaging the die.
If the die is packaged in a surface mount package, such as a standard ball grid array package, there is little constraint on the height of the wire loop as the package encapsulant formed over the wire bonds and die can simply be adjusted.
FIG. 4 is diagrammatic illustration of a cross-sectional view of a portion of a ball grid array package having a die with bond pads wire bonded to the package substrate. Package 400 includes a substrate 402 having a die 404 mounted on the top surface. Bond pads 406 are connected to bond fingers (not shown) formed on the surface of the substrate 402 by bonding wires 408. The bond fingers are typically interconnected to associated vias 410 formed through the substrate 402 to provide conductive interconnection of the die 404 to the external package contacts 412. Typically, an encapsulant 416, e.g., a plastic cap, is molded over the die 404 and the bonding wires 408.
As illustrated, the height of the wire loop of the bonding wire 408 is maintained within the encapsulant 416. When assembling a die having staggered bond pads, the wire loop heights may need to be adjusted to prevent the bonding wires from contacting each other. Encapsulation of the bonding wires can be maintained by adjusting the height of the encapsulant 416.
Unfortunately, while this package presents little constraints on loop heights of the bonding wires, it has limited heat dissipation capability. Thus, for dice requiring higher heat dissipation or other package properties, especially high-density dice that utilize staggered bond pads, other package structures have been developed. Many of these designs mount the die within a cavity in the substrate so that the die is thermally connected to a heat dissipating layer of the substrate. The package may then be mounted on another substrate, such as a printed circuit board, so that the heat dissipating layer is facing out.
FIG. 5 is a diagrammatic illustration of a cross-sectional view of a portion of a single-tier thermally enhanced ball grid array-type package having a die mounted in a die cavity formed in the package substrate. Package 500 includes a substrate 502 having a die 504 located in a die cavity 506. The substrate 502 includes a heat dissipating layer 508, such as a copper plate, and the cavity 506 is formed in the surface of the substrate 502 exposing a portion of the heat dissipating layer 508 within the cavity 506. The die 504 is mounted within the die cavity 506 and thermally connected to the heat dissipating layer 508 of the substrate 502. Bond pads 510 on the die 504 may be electrically connected to the substrate 502 by bonding wires 512 to bond fingers (not shown) formed on the top surface of the substrate 502. In some packages, there may be multiple rows of bond fingers. Conductive traces routed across the surface of the substrate 502 electrically interconnect the bond fingers to contact landings (not shown) on which contacts 514, such solder balls, are formed. An encapsulant 516 is formed over the die 504 and bonding wires 512. When the package 500 is interconnected to another substrate, such as a printed circuit board, it is mounted cavity down to allow electrical interconnection of the package through the contacts 514, and heat dissipation through the heat dissipating layer 508.
While this package provides the needed heat dissipation and is commonly inexpensive to manufacture, a minimum clearance height 518 cannot be exceeded by the encapsulant 516 in order that the contacts 514 successfully bond to the other substrate. Thus, any bonding wires 512 also cannot exceed this minimum clearance height 518, as they must be maintained within the encapsulant 516.
When assembling a die having staggered bond pads, this minimum clearance height limits the height of bonding wires. Although different loop heights may be used, these heights are restricted and where bonding wires cross over one another, the vertical separation may be small. Often the encapsulation process results in wire sag which may cause the longer bonding wires to contact other bonding wires that are crossed over. This results in shorting and yield loss during production. Thus, although this form of packaging is inexpensive, it is difficult to use with a die having staggered bond pads as the minimum clearance height restricts the adjustment of loop heights.
Some developers have attempted to assemble staggered die into these packages by utilizing complex wire loops with multiple kinks to effect the use of smaller, more rigid wire xe2x80x9cloopxe2x80x9d heights, but this process is typically very expensive with poor yields. Other developers have turned to multi-tier enhanced ball grid array packages to avoid the minimum clearance height constraints.
FIG. 6 is a diagrammatic illustration of cross-sectional view of a portion of a multi-tiered thermally enhanced ball grid array-type package having a die with bond pads wire bonded to the package substrate. Package 600 includes a substrate 602 having a die 604 located in a die cavity 606. The substrate 602 may be multi-layered and includes a heat dissipating layer 608, such as a copper slug. The cavity 606 is formed in the surface of the substrate 602 exposing a portion of the heat dissipating layer 608 within the cavity 606. The die 604 is mounted within the die cavity 606 and thermally connected to the heat dissipating layer 608 of the substrate 602. Bond pads 612 of the die 604 are electrically connected to bonding rings or bond fingers, not shown, located on the tiers 616 and 618 of the substrate 602 by bonding wires 614. The bond fingers and bonding rings are connected to external contacts 620, such solder balls, via associated conductive traces and vias formed in the substrate 602. An encapsulant 622 is formed over the die 604 and wire bonds 614 filling the cavity 606. When the package 600 is interconnected to another substrate, such as a printed circuit board, it is mounted cavity down.
As illustrated, there is a greater height within the cavity 606 within which to adjust the loop height of the bonding wires 614. When assembling a die having staggered bond pads, it is much easier to avoid wire contact between bonding wires that cross over by adjusting the loop heights. Further, as many of the bonding wires may be associated with different tiers, the chance of contact between the bonding wires can be further reduced. Thus, the multi-tier package provides the needed heat dissipation, and has reduced wire loop height constraints over that of the single-tier cavity package of FIG. 5, however, a disadvantage of multi-tiered cavity packages is that they are currently about one and a half times more expensive than the single-tier ball grid array package.
Thus, it would desirable to have a method and/or device that would allow assembling of die having staggered bond pads into single-tier thermally enhanced ball grid array packages.
In accordance with the present invention, there is described an integrated circuit package having a die with outer bond pads and inner bond pads, where at least some of the inner bond pads are staggered relative to the outer bond pads. The package has three supply rings and bond fingers formed external to the third supply ring. The bond pads of the die are connected to associated supply rings and bond fingers of the package according to a design methodology where, in one embodiment, at least all bond pads connected to the supply rings are outer bond pads, and the staggered inner bond pads are connected to bond fingers. The loop height of the bonding wires from the outer bond pads connected to the supply rings is lower than the loop height of the bonding wires from the staggered inner bond pads to prevent wire contact.
According to another embodiment, there is described a method for assigning and positioning the bond pads of the die to allow assembly of the die into a single-tier package and to prevent wire contact.
According to a further embodiment, there is described a die having outer bond pads and staggered inner bond pads, formed in accordance with the method of the present invention.